Page 303 - Organic Electronics in Sensors and Biotechnology

280 Chapter Seven

the organic material deposition. The achievable tuning range is pri-
66
marily limited by the optical gain spectrum of the material. Other
influences such as absorption of the substrate, deviations in the lat-
tice form and the lattice period, the grating design (e.g., the duty cyle)
itself, and the quality of the laser resonator may restrict the range
further and increase the laser threshold to unacceptable levels.

7.4 Integrated Optical Sensor Systems
The examination of biological and chemical samples is essential for
medicine, biology, and environmental monitoring. These analyses
normally take place in central laboratories. In recent years, a clear
trend toward miniaturized analytical devices, which are applicable at
the “point of care,” is recognizable.
This chapter deals with the integration of organic laser sources
into such systems. The technology of miniaturized optical sensor sys-
tems will be introduced with respect to the possible use of organic
lasers. Different sensing schemes that are relevant for laser-based
analysis systems will be described including a short summary of
waveguide and microfluidic based systems. The last part describes
the work on the first waveguide coupled organic semiconductor
lasers that are based on low-cost polymeric substrates.
7.4.1 Sensing Schemes
The miniaturization of bioanalytical techniques has an enormous rel-
evance for the rapidly growing life sciences. Therefore, the realization
of so-called lab-on-a-chip or micro total analysis system (μTAS) has
become an important goal during the last years. This section dis-
cusses the major optical sensing principles which could be incorpo-
rated into such a system making use of an integrated laser source.
The determination of biological, physical, or chemical parame-
67
ters such as molecule type, binding behavior, or concentration can
be realized by the optical investigation of
1. Absorbance and reflectance
2. Fluorescence
3. Interference phenomena
4. Resonance phenomena
The optical sensor consists preferably of a laser as a light source,
the sensing setup, and a detector. See Fig. 7.12.

Tunable laser source Sensing system Detector

FIGURE 7.12 Sensing scheme of an optical sensor.